10/9/2010
CONTENT SCHEDULE – 5th Meeting
Civil Engineering Materials 1. Types and application of steel in construction SAB 2112 2. Non-ferrous metal - types and characteristics, use of non-ferrous metal in construction Introduction to Steel 3. Latest constructiilion materials - polllymer, glass, composite material, cement based products
Dr Mohamad Syazli Fathi
Department of Civil Engineering RAZAK School of Engineering & Advanced Technology UTM International Campus
October 9, 2010
Learning Objectives Introduction: Steel
1. Understand different types of structural steels used in • Steels are essentially alloys of iron and carbon but they construction. always contain other elements, either as impurities or alloying 2. Discuss about the stress-strain relationship of structural elements. steel. • Steel is man made metal containing 95% or more iron and 1 – 3. Highlight the advantages and disadvantages of using steel 2% carbon, smaller amounts (around 1.6%) of manganese, nickel to improve certain properties. as structural material. • Carbon improves strength/hardness but reduces ductility and 4. Discuss fatigue failure and it’s significance. toughness. 5. Brittle fracture of steel. • Low carbon steels are not used as structural materials. 6. Fire performance and protection of the steel. • Alloying nickel, the tensile strength can be increased while retaining the desired ductility. 7. Corrosion of steel and it’s protection.
Types of Steel Low Carbon Steel
Also known as mild steel Steel Contain 0.05% -0.32% carbon 1. Tough, ductile and malleable •Low carbon steel (mild steel) 2. Easily joined and welded •Medium carbon steel 3. Poor resistance to corrosion •High carbon steel (tool steels) 4. Often used a general purpose material •Cast iron •Nails, screws, car bodies, Alloy Steels •Structural Steel used in the construction industry
•High speed steel 5 6
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Medium Carbon Steel High Carbon Steel
Contains 0.35% - 0.5% of carbon Also known as ‘tool steel’ Contain 0.55%-1.5% carbon Offer more strength and hardness BUT less ductile and malleable Very hard but offers Higher ShdilStrength Less ductile Structural steel, rails and garden tools and less malleable
Hand tools (chisels, punches) Saw blades
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Cast Iron Introduction: Steel
Contains 2%-4% of carbon • Steel as building material has been used in various types of Very hard and brittle structures: Strong under compression 1. Multi-storey building skeleton Suitable for casting [can be pour at a relatively low temperature]
Engine block, engineer vices, machine parts
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Introduction: Steel Introduction: Steel
1. Multi-storey building skeleton • Steel as building material has been used in various types of structures: 2. Industrial buildings
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Introduction: Steel Introduction: Steel
• Steel as building material has been used in various types of • Steel as building material has been used in various types of structures: structures: 3. Transmission towers 4. Railway bridges
Advantages of steel as a structural Introduction: Steel material
1. High strength to low weight - good for long span bridges, tall • Steel as building material has been used in various types of buildings. structures: 2. Lightweight compared to concrete - can be handled and transported, 5. Reinforced concrete steel rebar and prefabricated. 3. PlProperly maiidintained have a long life. 4. Uniformity properties do not change with time. 5. A ductile material, does not fail suddenly, but gives visible evidence of failure by large deflections. 6. Additions and alterations can be made easily. 7. They can be erected at a faster rate compared to reinforced concrete. 8. Steel has the highest scrap value. 9. Can be even reuse on demolition.
Advantages of steel as a Advantages of steel as a structural material structural material
1. Lightweight compared to concrete - can be handled and transported, and prefabricated. 2. Properly maintained have a long life. 3. Uniformity properties do not change with time. 1. High strength to low weight - good for 4. A ductile material, does not fail suddenly, but gives visible evidence long span bridges, tall buildings. of failure by large deflections.
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Advantages of steel as a structural material Disadvantages of steel as a structural material
1. When placed in exposed conditions, are subjected to corrosion. They require painting, hence induce high maintenance cost. 2. Needs fire proof treatment, which increase cost 3. Fatigue – strength reduced if large number of stress 1. Additions and alterations can be made reversals.. easily. 2. They can be erected at a faster rate compared to reinforced concrete. 3. Steel has the highest scrap value. 4. Can be even reuse on demolition.
Disadvantages of steel as a structural material Disadvantages of steel as a structural material
1. When placed in exposed conditions, are subjected to corrosion. They require painting, hence induce high maintenance cost. 2. Needs fire proof treatment, which increase cost.
Disadvantages of steel as Types of steel a structural material
Carbon Steel • Carbon steel, also known as plain carbon steel, is steel where the main alloying constituent is carbon. • According to American Iron and Steel Institute (AISI), they defines carbon steel as: “Steel is considered to be carbon steel when – no minimum content is specified or required for chromium, cobalt, columbium, molybdenum, nickel, titanium, tungsten, vanadium or zirconium, or any other element to be added to obtain a desired alloying effect; – when the specified minimum for copper does not exceed 0.40 percent;or Source: http://global-sei.com/sn/2007/352/4.html when the maximum content specified for any of the following elements does not exceed the percentages noted: manganese 1.65, silicon 0.60, copper 0.60.” 3. Fatigue – strength reduced if large number of stress • Carbon has the maximum influence on the mechanical properties of reversals. steel. Steel with a low carbon content has properties similar to iron.
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Types of steel Types of steel
Carbon Steel • As the carbon content rises, the metal becomes harder and Alloy Steel stronger but less ductile and more difficult to weld. • Alloy steel is steel alloyed with a variety of elements in amounts of •In gg,general, higher carbon content lowers the meltin gpg point and between 1 and 50% byy weight to improve its mechanical ppproperties. its temperature resistance. • Alloy steels are broken down into two groups: • There are generally 3 classes depend on carbon content: – Low Alloy Steel – High Alloy Steel – Mild Steel (up to 0.25%) • Most commonly used alloy steel are low alloy steel. – Medium Carbon Steel (0.25% to 0.45%) – High Carbon Steel (0.45% to 1.50%) • Alloy steels have greater strength, hardness, hot hardness, wear • Mild steel is the most common use because its price is resistance, hardenability, or toughness compared to carbon steel. relatively low while it provides material properties that are • However, they may require heat treatment to achieve such properties. acceptable for many applications. Common alloying elements are molybdenum, manganese, nickel, chromium, vanadium, silicon and boron.
Types of steel Types of steel Stainless Steel • In metallurgy term, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass. • Stainless steel does not stain, corrode, or rust as easily as ordinary steel (it stains less, but it is not stain-proof). It is also called corrosion-resistant steel or CRES Tool Steel when the alloy type and grade are not detailed, particularly in the aviation industry. • There are diff erent grad es and surf ace fi fiihnishes of stai ilnless steel to sui t th e • Tool steel refers to a variety of carbon and alloy steels that environment to which the material will be subjected in its lifetime. Stainless steel is are particularly well-suited to be made into tools. used where the properties of steel, and resistance to corrosion are required. • Their suitability comes from their distinctive hardness, • Stainless steel differs from carbon steel by the amount of chromium present. • Carbon steel rusts when exposed to air and moisture. Stainless steels contain resistance to abrasion, their ability to hold a cutting edge, sufficient chromium to form a passive film of chromium oxide, which prevents and/or their resistance to deformation at elevated further surface corrosion and blocks corrosion from spreading into the metal's temperatures. internal structure. • Tool steel is generally used in a heat-treated state.
Structural Steels
• Structural steel is made up of about 98% of iron with the main alloying elements – carbon, silicon and manganese. • Copper and chromium are added to produce weather- resistant steels that do not require corrosion protection. • Main design property of structural steel is based on the yield strength of the steel, but other properties including ductility, toughness, impact resistance and weldability are also important.
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Structural Steel Sections • Hot Rolled Section – UB, UC sections, channel, T, angle, tube, bars, flats, plates, sheets, and strips.
Structural Steel Sections
• Compound Section – combination of two or more sections to strengthen the structural member.
Structural Steel Sections Structural Steel Sections • Built-up/Fabricated Section – Built-up sections are made • Cold Rolled/Formed Section – Cold-formed steel by welding plates together to form I, H or box members structural members are shapes commonly manufactured which are termed plate girders, built-up columns, box from steel plate, sheet or strip material. Examples of the girders or column, respectively. cold-formed sections are corrugated steel roof, floor decks, steel wall panels, storage racks and steel wall studs.
Fabricated sections can be welded or bolted
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Stress-Strain Relationship of Steel Stress-Strain Relationship of Steel Prior to the yield point, the material will deform elastically and (C’ will return to its (E ) original shape when the ) applied stress is (F removed. )
Once the yield point is (C (D passed some fraction of ) ) the deformation will be permanent and non- reversible. • Yield strength is defined as the stress at which a material begins to deform plastically. The stress at which material strain changes from elastic deformation to plastic deformation, causing it to deform permanently.
Grade of Steel and Design Steel Properties Strength
Grade of Steel Yield Strength or Design • The mechanical properties of steel largely depend on its chemical 2 composition, rolling methods, rolling thickness, heat treatment, stress Strength(N/mm ) history, and thermal expansion (α) Grade 55 S460 460 Property Value 2 Grade 50 S355 355 Yield stress fy 220 – 540 N/mm
Grade 43 S275 275 Ultimate tensile strength 1.2 fy
• Structural steel is basically produced in 3 strength grades; there are S275, % Elongation (Low carbon steel) 20 S355 and S460. Modulus of elasticity (E) 2 X 105 N/mm2 • S460 is the strongest, but the lower grade S275 is the most commonly used in structural applications. Shear modulus (G) 0.4 E • S stands for “Structural”. Poisson’s ratio (µ ) 2 • The number indicates the yield strength of the material in N/mm . a) elastic range 0.3 b) plastic range 0.5
Fatigue Brittle Fracture 1. Fatigue failure can occur in members or structures subjected to fluctuating loads such as crane girders, bridges and offshore 1. Structural steel is ductile at temperatures above 10oC but it becomes structures. more brittle as the temperature falls, and fracture can occur at low 2. Fatigue is damage caused by repeated fluctuations of stress leading to stresses below 0oC. gradual cracking of a structural element. 2. The Charpy impact test is used to determine the resistance of steel to 3. Failure occurs through initiation and propagation of a crack that brittle fracture. starts at a fault or structural discontinuity and the failure load may be 3. Brittle fracture can be avoided by using steel quality grade with well below its static value. adequate impact toughness. Quality steels are designated JR, J0, J2, 4. Welded connections have the greatest effect on the fatigue strength of K2 in order of increasing resistance to brittle fracture. steel structure. On the other hand, bolted connections do not reduce 4. Beside the selection of steel grade, attention should also be focused the strength under fatigue loading. on design details. Such as: 5. To help avoid fatigue failure, detail should be such that stress 1. Thin plates are more resistant than thick ones. concentrations and abrupt changes of section are avoided in regions 2. Abrupt changes of section and stress concentration should be avoided. of tensile stress. 3. Fillet welds should not be laid down across tension flanges. 4. Intermittent welding should not be used.
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Brittle Fracture
• Brittle fracture occurs when critical combinations of the following exist: – A severe stress concentration due to severe structural discontinuity. – A significant tensile force occurs. – Low fracture toughness at service temperature. – Dynamic loading.
• In general, designing structures so that they only incorporate details that provide good fatigue performance is a very effective way of reducing brittle fracture.
Fire Performance and Protection Fire Performance and Protection
• The performance of steel in fire depends on: 1. The severity of the fire 2. The protection applied to the steel 3. The loads applied to the steel 4. The size and properties of the steel members
• Structural steelwork performs badly in fires, with the strength decreasing with increase in temperature. • At 550oC, the yield stress has fallen to approximately 0.7 of its value at normal temperatures – that is, it has reached its working stress and failure occurs under working loads.
Fire Performance and Protection
• Fire protection can be provided by encasing the member in concrete, fire board or cementitious fibre materials. • Recently, intumescent paint is being used especially for exposed steelwork. Intumescent paint : • It means that the paint does a lot more than simply decorate. At the first lick of a flame, the properly- coated surface that looks like any standard good quality paint job instantly starts to “intumescent”- to swell, to bulge-up into a solid foam. A film six mils thick (about 2 cigarette papers) will swell up to make almost an inch thick layer of black foam. With the first hot flash, on any surface protected
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Corrosion Protection Corrosion Protection
1. Exposed steelwork can be severely affected by corrosion in 3. The type of protection depends on the surface conditions the atmosphere, particularly if pollutants are present, and it and length of life required. is necessary to provide surface protection in all cases. 2. Many types of steel, ildiincluding most common grades of 4. Themain types of prottitective coatings are: structural steel will corrode if exposed to moisture and 1. Metallic coatings: Either a sprayed-on in line coating of oxygen. If either or both of these are prevented from aluminium or zinc is used or the member is coated by hot-dipping contacting the steel it will not corrode under normal it in a bath of molten zinc in the galvanising process. circumstances. 2. Painting: Where various systems are used. One common system consists of using a primer of zinc chromate followed by finishing costs of micaceous iron oxide. Plastic and bituminous paints are used in special cases.
More Info: http://www.worldsteel.org/
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